Recently, cardiac pacing protocols employed by implantable cardiac pacemakers and implantable cardioverter defibrillators (ICDs) are aimed at promoting intrinsic conduction and intrinsic depolarization of the ventricles as often as possible while reducing or minimizing ventricular pacing. Such a pacing protocol generally includes pacing in an atrial mode, such as AAI, ADI, AAIR or ADIR mode, while monitoring intrinsic AV conduction. As long as AV conduction is intact, the atrial pacing mode is maintained. If AV conduction is absent, ventricular pacing is delivered, for example in a dual chamber pacing mode such as DDI or DDIR, to ensure ventricular depolarization during AV block.
Many patients implanted with cardiac pacemakers or ICDs have underlying coronary artery disease and are susceptible to myocardial ischemia. When the pacing mode is programmed in a rate responsive mode (e.g. ADIR, DDDR, or DDIR), a higher pacing rate is provided in response to a sensed increase in metabolic need. The higher pacing rate increases the metabolic demand placed on the myocardium, which could lead to ischemia. Patients subjected to minimum ventricular pacing may have long AV conduction times that result in inefficient AV coupling. Inefficient AV coupling can adversely affect cardiac output and subsequently reduce myocardial perfusion leading to myocardial ischemia. Other causes of myocardial ischemia may be disease related. It is desirable to provide cardiac pacing in a manner that does not worsen an ischemic state and may act to alleviate myocardial ischemia.